S. N. Shamin

Experimental and theoretical investigation of the electronic structure of transition metal sulphides: CuS, and

Results of measurements of sulphur x-ray emission spectra of CuS and , excited by synchrotron radiation near the sulphur 2p threshold, are presented. An excitation energy dependence of the sulphur XES is only observed for CuS, and is attributed to the presence of inequivalent sulphur atoms in CuS. Two thirds of the sulphur atoms form dimers (as in ) while the remaining ones are single (as in ). This conclusion is confirmed by XPS measurements and LMTO band structure calculations for CuS, and . It is shown that selective excitation of x-ray emission valence spectra can be used to determine the atom-decomposed partial density of states for inequivalent sites in solids, occupied by chemically identical species.

Electronic structure of FeCr2S4 and Fe0.5Cu0.5Cr2S4

A full study of the electronic structures of FeCr2S4 and Fe0.5Cu0.5Cr2S4 is reported based on x-ray photoelectron spectra (valence band and core levels), x-ray emission spectra (Fe Lα, Cu Lα, Cr Lα, S Kβ1,3 and S L2,3) and ab initio TB-LMTO band structure calculations. In the valence band of FeCr2S4, the Fe 3d states are found to be more localized than the Cr 3d states, which dominate at the Fermi level. In Fe0.5Cu0.5Cr2S4, the distribution of Cr 3d (Cr3+) states is unchanged and the Cu ions were found to be in the Cu+ state.

Valence band spectra of 4d and 5d silicides

A full study of the electronic structure of 4d and 5d silicides (RuSi, RhSi, PdSi, OsSi, IrSi, , PtSi) is undertaken including XPS VB and XES ( and ) measurements and LMTO band structure calculations. It is found that d bands which dominate the density of states are more localized with increasing atomic number Z of the transition metal. A strong hybridization between silicon 3p and transition metal d states occurs over the entire valence band. Si 3s states are found to be not mixed with Si 3p and nd states but Si 3d states participate in bonding and hybridize with transition metal d states. The non-bonding character of the majority of nd states is not confirmed for 4d and 5d silicides.

CKα X-ray emission spectra of C60

Abstract The X-ray emission spectra of C 60 are studied with high energy resolution. We have found a great difference between the CKα XES of C 60 and those of diamond. On the other hand, the spectra of C 60 and of soot showed some similarity which provides evidence of sp 2 hybridized carbon bonds in C 60 . The results obtained are compared with photoemission measurements and theorerical calculations of the electronic structure of C 60 .

Application of high energy resolved X-ray emission spectroscopy for monitoring of silicide formation in Co/SiO2/Si system

Abstract High-energy resolved X-ray emission spectroscopy was used to study the influence of oxide thickness on the thermally-induced CoSi 2 - formation in the Co/SiO 2 /Si system. The Si L 2,3 X-ray emission spectra have shown different fine structure dependent on the thickness of the buried oxide layer, the annealing temperature and the time of annealing. A full analysis of silicidation is undertaken on the basis of comparison of the spectra of the samples under investigation with those of reference samples of c -Si, SiO 2 and CoSi 2 . It is found that silicidation in this system, with formation of CoSi 2 , starts at annealing temperatures above 900°C. Annealing at 1100°C for 10 s was required for formation of the CoSi 2 phase in the Co/SiO 2 /Si system with a 3-nm thick layer of SiO 2 . It is shown that increasing annealing time from 10 to 45 s leads to formation of CoSi 2 for thicker (about 10 nm) layers of SiO 2 .

Electronic structure of FeSi

A full set of high-energy spectroscopy measurements including x-ray photoelectron valence band spectra and soft x-ray emission valence band spectra of both components of FeSi (FeKbeta 5, FeLalpha , SiK( beta 1,3) and SiL2,3) are performed and compared with the results of ab initio band structure calculations using the linearized muffin-tin orbital method and the linearized augmented plane wave method.

X-ray emission spectra and interfacial solid-phase reactions in Hf/(001)Si system

High energy resolved X-ray emission spectroscopy with variable electron beam excitation is applied for the study of solid-phase reactions in the Hf/(001)Si system at different annealing temperatures. It is found that annealing at 700°C is accompanied by formation of HfSi. The HfSi2 phase is formed at 780°C. The formation of Hf silicides in depth is studied by measurements of Si L2,3 X-ray emission valence spectra under different accelerating voltages. The data obtained by means of X-ray emission spectroscopy are compared with those obtained by means of Rutherford backscattering and electron-probe microanalysis techniques.

Characterization of CNx-films by X-ray emission measurements

The local atomic bonding structure of carbon nitride films synthesized by the reactive ionized cluster beam method using X-ray emission spectra (XES) was examined. An ionized cluster beam system was used to prepare the carbon nitride films. The composition of carbon nitride films was measured with Rutherford backscattering spectroscopy techniques and the N/C ratio was found to be approximately 0.25. The XES measurements of the carbon nitride films showed a predominant proportion of sp bonded carbon and nitrogen atoms.

The influence of high-energy electron irradiation and boron implantation on the oxide thickness in the /Si system

The system exposed to irradiation with 11 - 12 MeV electrons was studied by soft-x-ray emission spectroscopy using the variable-exciting-electron-energy, optical ellipsometry, and nuclear reaction techniques. For the system prepared on an n-substrate, oxidation of Si was observed, and the thickness of the layer after electron irradiation was estimated. For the system prepared on a p-Si substrate, irradiation-induced oxidation was not observed. It was found that preliminary boron implantation in the -Si system blocks oxidation of the n-Si substrate exposed to electron irradiation.

Chemical reactions in polymers induced by ion beam mixing: fluorescence X-ray measurements

Fluorescent soft X-ray emission spectroscopy (XES) is used to study chemical reactions in polyimide (PI), poly- ethersulphone (PES) and polycarbosilane (PCS) films induced by ion-beam mixing. It is found that the fine structure of the 14 22 carbon XES of the PI and PES films is modified after irradiation with fluences above 1310 cm , which is attributed to the degradation of the molecular structure in amorphous C:N:O. The width of the electronic gap decreases with the ion fluence, in correlation with reported increase of conductivity and optical absorption. The bonding configuration of free carbon precipitated in a matrix of a-SiC after irradiation of PCS is closer to that of diamond-like carbon than in a film submitted to combined treatments of irradiation1annealing or direct annealing. Nevertheless clusters formed in the annealed 2 PCS films are less sp -hybridized than in silicidated graphite or sputtered Si:C:H films.